1. Field of the Invention
This invention relates generally to communication systems, and, more particularly, to wireless communication systems.
2. Description of the Related Art
In conventional wireless telecommunications, one or more mobile units (or access terminals) may establish a mobile communication path through a wireless communication link to a base station, which may also be referred to as a radio access network (RAN). A typical wireless communication link includes numerous uplink and downlink channels between the mobile units and the base station. For example, the wireless communication link may include uplink and downlink traffic channels for carrying data packets between the mobile unit and the base station, as well as uplink and downlink signaling channels for transmitting signaling information between the mobile unit and the base station. Signaling information typically includes information used to configure the mobile unit and/or the base station, as well as information used to maintain, operate, and/or modify the characteristics of one or more of the channels associated with the wireless communication link.
The channels of the wireless communication link are established according to one or more protocols, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), and the like. For example, Evolution, Data-Optimized (EV-DO) wireless communication systems combine features of CDMA and TDMA protocols to enhance overall system capacity. An EV-DO wireless communication system also implements other enhancements such as adaptive modulation and/or coding, incremental redundancy using the Hybrid Acknowledgment Request (H-ARQ) technique, and multiple high data transmission rates. Consequently, the signaling channels in an EV-DO wireless communication system may be used to provide information associated with the adaptive modulation and/or coding, incremental redundancy, data transmission rates, and the like.
One of the signaling channels implemented in a conventional EV-DO wireless communication system is a reverse rate indicator channel that provides information for implementing incremental redundancy and multiple data transmission rates. The reverse rate indicator channel is used to transmit information from the mobile unit to the base station. For example, incremental redundancy permits unsuccessfully decoded sub-packets to be retransmitted and combined with the previously transmitted sub-packets to improve decoding success rate. Each of the retransmitted sub-packets includes a sub-packet identifier. A data rate identifier is used to inform the base station of the data rate that the mobile unit is using to transmit packets. In an EV-DO wireless communication system, the sub-packet identifier and the data rate identifier are encoded together and transmitted over the reverse rate indicator channel.
The number of bits used to transmit the reverse rate indicator may be relatively large (e.g., six or more bits) because of a reverse rate indicator includes information indicative of both the sub-packet identifier and the data rate identifier. Moreover, the transmitted bits are generally different for each retransmission. For example, when a sub-packet is transmitted, the associated reverse rate indicator bits may be 111111. If a re-transmission of the sub-packet is requested, then the sub-packet and the associated reverse rate indicator may be retransmitted. However, the sub-packet identifier associated with the re-transmitted sub-packet will be different than the sub-packet identifier associated with the original sub-packet so that the associated reverse rate indicator will also be different. For example, the reverse rate indicator associated with the re-transmitted sub-packet may be 1111(−1)(−1). Consequently, the reverse rate indicators associated with multiple re-transmitted sub-packets cannot be literally accumulated to improve the detection rate for the reverse rate indicator channel. Although the detection reliability of the reverse rate indicator may be improved by increasing the reverse rate indicator channel transmit power, the increased reverse rate channel indicator gain also increases the Rise-over-Thermal and therefore limits data throughput on the reverse link.